Content:
Solar water heating system in Chew Magna


Our solar water heating system was installed in November 2003. This involved fixing 3 panels on the south facing roof of our cottage, replacing the hot water tank and carrying out some plumbing and wiring in the roof space and airing cupboard. It is a (pumped) heat exchange system circulating an antifreeze fluid initially heated by thirty six vacuum tube solar collectors.


The installation process required visits from a surveyor, an external (roof) fitter and an internal fitter, taking about 2 days in total. We also needed to call out the fitters in the months following the installation to eliminate minor leaks. There is a five year guarantee on the entire system.

PROs
The company that supplied our solar system (Smart Energy) claimed 'up to 40% saved on your heating bill'. No, I didn't believe it either, but last year we had no need for gas water heating from mid April to late October, which does represent a significant saving. The vacuum tube collector is particularly suited to our climate: the water is still warmed on bright cloudy days.

Fully automatic operation. We already had a separate hot water control with the gas CH , and a control box with a display is wired in to the system. This shows the hot water tank and the solar collector temperatures along with other readings, but this is for information and doesn't need any action to be taken!

In addition to the standard (gas) heat exchange coil, the new hot water tank has a separate, very efficient solar heated coil built into it. The positions of the coils and thermostats in the tank ensure that the sun always heats the water preferentially.

The solar water heating is silent, apart from a quiet hum from the pump in the roof. Our system required some leak fixing, but otherwise it is maintenance free. Notwithstanding accidental damage, it should carry on heating our water for a very long time.

CONs
The cost of the installation. You have to be interested in saving the planet as well as saving money! Our Smart Energy system cost over £6K. At the time, they seemed to be the only accessible suppliers of these highly efficient, vacuum tube solar collectors. At least one other company (Solar Sense) now supply this type of system at about half this cost: around £3K. However, don't expect a quick financial return on your investment! 

Inevitably, on those rare cloudless days, the water in the tank has reached its set maximum temperature in the morning. The circulating pump automatically cuts out leaving the solar collector to stew in the blazing sun without any heat exchange to cool it. At around 150 deg.C the pressurised, super heated water in the tubes reaches equilibrium. The system is designed to take this punishment (4 bar pressure), but the water in the tank will not be reheated - ie the pump resumes circulation- until the temperature of the circulation fluid has finally cooled to below boiling point.

NICK SCHOLEFIELD, THE CHALKS, CHEW MAGNA
contact me for more info: nickscholefield@waitrose.com [1]